Tatsuhiro Fukuba

A new drifting underwater camera system for observing spawning Japanese eels in the epipelagic zone along the West Mariana Ridge

Spawning-condition Japanese eels Anguilla japonica, fertilized eggs, and newly-hatched preleptocephali have been captured, and studies for observing spawning eels with underwater camera systems have begun. This study describes a new, less invasive, free-drifting underwater camera observation system that was deployed from the research vessel (R/V) Natsushima in June 2013. Three drifting buoy camera systems (Una-Cam) with lights-on/lights-off programmed sequencing during daytime and nighttime hours were deployed over a period of seven days at 20 locations south of a salinity front along the southern West Mariana Ridge. Live artificially matured A. japonica eels held in transparent chambers were used as an attractant source through the release of reproductive pheromones and other odors. Each system was suspended from a buoy array at a depth of 174–200xa0m, with four cameras and three lights pointed downward at different angles towards the eel chamber. The Una-Cam systems were stable and were effective at recording images of fish, crustaceans, and gelatinous zooplankton. Olfactory cues may have attracted male and female Derichthys serpentinus eels, which showed what seemed to be reproductive behavior and attraction to the Japanese eels in the chamber. Una-Cam systems are capable of recording images of anguillid eels, if they approach, and may be useful for observing spawning eels in their offshore spawning areas.

The Yoron Hole: The Shallowest Hydrothermal System in the Okinawa Trough

During NT10-16 cruise with R/V NATSUSHIMA and ROV HYPER-DOLPHIN in 2010, a new hydrothermal vent community was discovered at the Yoron Hole, where is the shallowest hydrothermal system in the known hydrothermal site found in the Okinawa Trough. The maximum temperature of clear smoker fluid was 247 °C, which was slightly lower than the boiling temperature (275 °C) of the seawater at the water pressure of 560-m water depth (5.6 MPa). Hydrothermal chimneys are composed of barite, sphalerite, galena, pyrite, chalcopyrite, and tetrahedrite. Although crustaceans and polychaetes were found around the hydrothermal vent, the diversity and population density were lower than that of the Iheya North Knoll and the Izena Hole hydrothermal sites.

Now you see me, now you don’t: observation of a squid hiding in its ink trail

Pelagic cephalopods such as squid change coloration for camouflage or release ink as a defensive mechanism while being attacked by predators, which may block the view of the predator, have noxious chemical effects, or act as a warning signal for other squid (Bush and Robison 2007; Derby 2007; Wood et al. 2010). Pulsed releases of ink can also create “pseudomorphs” in the shape of squid that may serve as decoys to confuse predators about the location of the actual squid (Bush and Robison 2007; Wood et al. 2010). Some aspects of deep-sea squid behavior, including releases of their ink, have been observed using remote operated vehicles (ROV) (Hunt et al. 2000; Bush and Robison 2007), but most species have not been studied.

Development of in situ microbial ATP analyzer and internal standard calibration method

Integrated and miniaturized in situ analyzers to estimate microbial biomass has been developed so far. The analyzer has the capability to perform the luciferin-luciferase bioluminescence reaction to determine the concentration of microbial adenosine-5-triphosphate (ATP). The latest analyzer had been mounted on an ROV and evaluated at deep-sea environments. In this study, the method for in situ calibration that utilizes caged ATP as an internal standard is proposed to improve reliability of the in situ analyzer. Experiments confirmed that caged ATP was photolyzed with appropriate reproducibility by using a simple microfluidic device with the UV-LED light source.

The Irabu Knoll: Hydrothermal Site at the Eastern Edge of the Yaeyama Graben

The Irabu Knoll hydrothermal vents were first discovered in 2000 during YK00-06 cruise using R/V YOKOSUKA and manned submersible SHINKAI 6500. The Irabu Knoll consists of three seamounts from 1,680 to 1,970-m in water depth. The Irabu Knoll is located in the Southern Okinawa Trough and is constructed from basalt as the host rock. Two hydrothermal venting sites have been found at East and West seamount. Sulfide deposit of the Irabu Knoll hydrothermal system consists of barite, sphalerite, pyrite, and chalcopyrite. Major taxa in the vent ecosystem are Shinkaia crosnieri, Munidopsis sp., and Ashinkailepsas sp.

Distribution and Biogeochemical Properties of Hydrothermal Plumes in the Rodriguez Triple Junction

In 2010, we conducted seven surveys for the deep-sea hydrothermal plume through conductivity-temperature-depth profiler (CTD) “tow-yo” cast in the area of the Kairei field. We observed a turbidity anomaly with a maximum thickness of 120 m, the upper limit of which was at 2,150 m water depth, approximately 300 m above the Kairei field hydrothermal vents (~2,440 m). The depth of upper limit of turbidity anomaly around Kairei field was the same height as in previous reports. Because the maximum height of hydrothermal plumes are regulated by the density (temperature and salinity) of the end-member hydrothermal fluid and dilution by the ambient seawater, the height of the plume suggested that the hydrothermal activity of the Kairei field was also the same as 17 years ago. Deep sequencing of microbial 16S rRNA genes showed that the SUP05 phylotypes and Epsilonproteobacteria, which are known as the potential sulfur oxidizer and/or possibly hydrogen oxidizer, were propagated in the early stage of the hydrothermal plume and in the hydrothermal fluid–seawater mixing zone near the Kairei hydrothermal vents. Our exploration found a hydrothermal plume at 14 km north of the Kairei field, which had different H2/CH4 ratio expected from the end-member hydrothermal fluid of Kairei field and the ambient seawater mixing. The north plume had a lower H2, higher CH4 concentration, and higher microbial cell density than those in the hydrothermal plume around Kairei field. The north hydrothermal plume represented too oxic condition to harbor methane production by anaerobic methanogens. In addition, our microbial community structure analysis based on deep sequencing of 16S rRNA genes more than 10,000-amplicon reads per one sample showed no signal of methanogenic archaea. This suggests little in situ methanogenesis from H2 in the plume. It seems likely that high concentration of methane in the north plume is derived from another hydrothermal plume source rather than the Kairei hydrothermal fluids. Further studies will be needed to understand the cause of high methane concentration in the north plume.

Underwater atomic force microscope

We developed a novel underwater atomic force microscopy (UAFM) system that is mountable on underwater vehicles or submersible seafloor platforms. This system is intended for in situ observation of microorganisms and microparticulates suspended and dispersed in deepwater near hydrothermally active features, with nanometer-scale spatial resolution. The system is composed of several technological elements: the main unit of the UAFM system, fluidic devices for sample collection from deepwater (e.g., pumps and a filtration unit equipped with membrane filters), and robust mounting mechanisms for the underwater vehicles or submersible seafloor platforms. We also use a commercially available self-sensitive cantilever as the AFM probe to detect cantilever deflection. To insulate the integrated piezoresistive gauges on the cantilever surface from the seawater under high pressure in deep sea, we applied thin coatings of poly(p-xylylene) polymer (Parylene) onto the cantilever surface. We successfully balanced the imaging quality and insulation performance by optimizing the conditions of the layer formation, i.e., the Parylene dimer type, temperature, and final layer thickness. Moreover, we invented a novel UAFM sample stage equipped with a sample filtration system based on membrane filters. To demonstrate the effectiveness of the sample stage with membrane filters in deep sea exploration, microorganisms suspended and dispersed in deepwater were successfully collected and fixed on the membrane filter. The developed UAFM system would be a useful tool for in situ observation of living microorganisms and microparticulates at nanoscale spatial resolution, possibly leading to new findings in deep sea.

Underwater atomic force microscopy for in situ observation of microorganisms in the deep sea

We present a novel underwater atomic force microscope system (underwater AFM system), which is mountable on underwater vehicles or submersible seafloor platforms. The mission of the system is to observe microorganisms and microparticulates in situ, which are suspended and dispersed in deepwater, with high spatial resolution down to nanometer scale. The system is composed of three major technological elements: a main unit of the underwater AFM, fluidic devices for the sample collection from deepwater (for example, pumps and a filtration unit using membrane filters), and robust mounting mechanisms for the underwater vehicles or the submersible seafloor platforms. Since we use a commercially available self-sensitive cantilever as the AFM probe, the deflection of the cantilever is measured by the integrated piezoresistive gauges. For insulation of the self-sensitive cantilever from the seawater under high pressure in the deep sea, we applied a thin layer coating of poly(p-xylylene) polymers (Parylene) onto the cantilever. We have successfully balanced the imaging quality and the insulation performance by optimizing the conditions of the layer formation, for example dimmer types of Parylene and the final layer thickness. We also have invented a novel sample stage for the underwater AFM equipped with a sample filtration mechanism using membrane filters. As a test result of the sample stage with the membrane filters in the deep sea exploration, the microorganisms suspended and dispersed in the deepwater have been successfully collected and fixed on the membrane filter. The present underwater AFM system would be a useful tool for in situ observation of the living microorganisms and microparticulates with nanoscale spatial resolution leading to future new findings in the deep sea.